A nucleic acid synthesis method, in particular a polymerase chain reaction (PCR) method, is a technique for simply amplifying a nucleic acid fragment of interest in a test tube, and recently becomes an essential experimental means not only for genetic research but also in a wide variety of fields in biology, medicine, and agriculture.
A nucleic acid synthesis reaction using a DNA polymerase such as PCR often has a problem with its reactivity such as specificity. In order to avoid a non-specific nucleic acid synthesis reaction, development of novel DNA polymerases, improvement of primer design methods, optimization of reaction solution composition, addition of compounds, and the like are attempted. For example, addition of betaine is found to be effective in amplifying CG-rich templates (Nonpatent Literatures 1 and 2).